Low temperature melt-processing of organic-inorganic hybrid

ABSTRACT

The present invention provides a process for preparing a melt-processed organic-inorganic hybrid material including the steps of maintaining a solid organic-inorganic hybrid material at a temperature above the melting point but below the decomposition temperature of the organic-inorganic hybrid material for a period of time sufficient to form a uniform melt and thereafter, cooling the uniform melt to an ambient temperature under conditions sufficient to produce the melt-processed organic-inorganic hybrid material.

This application is a Divisional of U.S. application Ser. No. 10/094,351filed Mar. 8, 2002, now U.S. Pat. No. 7,105,360.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for preparing amelt-processed organic-inorganic hybrid material and a method ofpreparing an improved field-effect transistor including a melt-processedorganic-inorganic hybrid material. More particularly, the presentinvention relates to a process for preparing a melt-processed perovskitematerial and a method of preparing an improved field-effect transistorincluding a melt-processed perovskite material.

2. Description of the Prior Art

Organic materials have received considerable recent attention aspotential replacements for inorganic counterparts in flat panel displaydriver circuitry and light-emitting elements, as well as for enablingtechnology for flexible and low-cost electronic devices. Organicmaterials have the advantage of simple and low-temperature thin-filmprocessing through inexpensive techniques such as spin coating, ink jetprinting, or stamping. In addition, the flexibility of organic chemistryenables the formation of organic molecules with useful luminescent andconducting properties. Since the first consideration of organicelectroluminescence (EL) devices over 30 years ago (J. Dresner, RCA Rev.30, 322 (1969)), organic light-emitting devices (OLEDs) have been widelypursued and near-commercial dot-matrix displays have recently beendemonstrated (T. Wakimoto, et. al., J. Soc. Info. Display 5, 235(1997)). In addition to emitting light, the semiconducting properties ofsome organic materials enable promising technologies for organic fieldeffect transistors (OFETs). Over the last few years, the carriermobilities of organic channel layers in OFETs have increaseddramatically from <10⁻⁴ to ˜1 cm²N-sec (comparable to amorphous silicon)(S. F. Nelson, et. al., Appl. Phys. Lett. 72, 1854 (1998) and C. D.Dimitrakopoulos, et. al., Science 283, 822 (1999)).

While promising with regard to processing, cost, and weightconsiderations, organic compounds generally have a number ofdisadvantages, including poor thermal and mechanical stability.Electrical transport in organic materials has improved substantiallyover the last 15 years. However, the mobility is fundamentally limitedby the weak van der Waals interactions between organic molecules (asopposed to the stronger covalent and ionic forces found in extendedinorganic systems). In OLEDs, the stability and mobility limitationslead to reduced device lifetime. For OFETs, the inherent upper bound onelectrical mobility translates to a cap on switching speeds andtherefore on the types of applications that might employ the low-costorganic devices. If these issues could adequately be addressed, newtechnologies might be enabled by alternative semiconductors, includinglight, flexible displays or electronics constructed entirely on plastic.

Organic-inorganic hybrid materials, including particularly materials ofthe perovskite family, represent an alternative class of materials thatmay combine desirable physical properties characteristic of both organicand inorganic components within a single molecular-scale composite.

The basic structural motif of the perovskite family is the ABX₃structure, which has a three-dimensional network of corner-sharing BX₆octahedra. The B component in the ABX₃ structure is a metal cation thatcan adopt an octahedral coordination of X anions. The A cation issituated in the 12-fold coordinated holes between the BX₆ octahedra andis most commonly inorganic. By replacing the inorganic A cation with anorganic cation, an organic-inorganic hybrid perovskite can be formed.

In these ionic compounds, the organic component is an intimate part ofthe structure, since the structure actually depends on the organiccation for charge neutrality. Therefore, such compounds conform tospecific stoichiometries. For example, if X is a monovalent anion suchas a halide, and A is a monovalent cation, then B should be a divalentmetal. Layered, two-dimensional A₂BX₄, ABX₄ and one-dimensional A₃BX₅,A₂A′BX₅ perovskites also exist and are considered derivatives of thethree-dimensional parent family.

The layered perovskites can be viewed as derivatives of thethree-dimensional parent members, with y-layer-thick cuts, i.e., y=1, 2,3 or more, from the three-dimensional structure interleaved with organicmodulation layers. The layered compounds generally have inorganic layerswith either <100> or <110> orientation relative to the originalthree-dimensional perovskite structure.

One <100>-oriented family of organic-inorganic perovskites has thegeneral layered formula:(R—NH₃)₂A_(y−1)M_(y)X₃₊₁where M is a divalent metal, X is a halogen atom (i.e. Cl, Br, I), A isa small inorganic or organic cation (e.g. Cs⁺, CH₃NH₃ ⁺), R—NH₃ ⁺ is alarger aliphatic or aromatic mono-ammonium cation, and y is an integerdefining the thickness of the inorganic layers. In this system, theammonium group is hydrogen-bonded and ionically bonded to the inorganicsheet halogens, with the organic tail extending into the space betweenthe layers and holding the structure together via Van der Waalsinteractions.

The (R—NH₃)₂MX₄ (y=1) members of this family include the simplest andmost numerous examples of organic-inorganic perovskites. Similar y=1 (orhigher y) layered perovskite structures can also be stabilized bydiammonium cations, yielding compounds with the general formula(NH₃—R—NH₃)MX₄. In these systems, there is no Van der Waals gap betweenthe layers since the ammonium groups of each organic layer hydrogen bondto two adjacent inorganic layers.

D. B. Mitzi, Prog. Inorg. Chem., 48, 1 (1999) reviews the state of theart and describes organic-inorganic perovskites that combine the usefulproperties of organic and inorganic materials within a singlemolecular-scale composite. U.S. Pat. No. 5,882,548 to Liang et al.describes solid state preparation of perovskites based on divalent metalhalide sheets. U.S. Pat. No. 6,180,956 B1 to Chondroudis et al. and C.R. Kagan et al., Science, 286, 945 (1999) describe integrating theself-assembling nature of organic materials with the high carriermobilities characteristic of inorganic materials for possible use inOrganic-Inorganic Field-Effect Transistors (OIFET's). Asemiconductor-metal transition and high carrier mobility in the layeredorganic-inorganic perovskites based on a tin(II) iodide framework havealso been described. These materials may be used as channel materialsfor field-effect transistors. K. Chondroudis et al., Chem. Mater.; 11,3028 (1999) describe single crystals and thin films of the hybridperovskites, which can be employed in Organic-Inorganic Light-EmittingDevices (OILED's).

The organic-inorganic hybrid materials, such as perovskites, may beprocessed to produce organic-inorganic perovskite crystals or thin filmsby conventional methods including the solution-based or evaporativetechniques described by D. B. Mitzi in the previously cited Prog. Inorg.Chem., 48, 1 (1999) and by Liang et al. in U.S. Pat. No. 5,871,579.However, these methods suffer from being high cost processing methodsand generally require the use of environmentally hazardous solvents.

Accordingly, it is an object of the present invention to providelow-cost, melt-processed organic-inorganic hybrid materials, which canbe used in a variety of applications, including flat panel displays,non-linear optical/photoconductive devices, chemical sensors, emittingand charge transporting layers in organic-inorganic light-emittingdiodes, organic-inorganic thin-film transistors and as channel layers inorganic-inorganic field-effect transistors.

These and other objects of the present invention will become apparent bythe novel perovskite compositions and the methods of preparing theperovskite compositions.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing a melt-processedorganic-inorganic hybrid material including the steps of:

maintaining an organic-inorganic hybrid material at a temperature abovethe melting point but below the decomposition temperature of theorganic-inorganic hybrid material for a period of time sufficient toform a uniform melt; and

cooling the uniform melt to an ambient temperature under conditionssufficient to produce the melt-processed organic-inorganic hybridmaterial.

The present invention further provides a process for preparing amelt-processed organic-inorganic hybrid material including the steps of:

applying onto a substrate an organic-inorganic hybrid material;

maintaining the substrate and/or the organic-inorganic hybrid materialat a temperature above the melting point of the organic-inorganic hybridmaterial but below the decomposition temperature of theorganic-inorganic hybrid material and the substrate for a period of timesufficient to form a uniform melt; and

cooling the substrate and/or uniform melt to an ambient temperatureunder conditions sufficient to form the melt-processed organic-inorganichybrid material.

The present invention still further provides a process for preparing alaminated melt-processed organic-inorganic hybrid material, includingthe steps of:

applying onto a substrate an organic-inorganic hybrid material;

maintaining the substrate and/or the organic-inorganic hybrid materialat a temperature above the melting point of the organic-inorganic hybridmaterial but below the decomposition temperature of theorganic-inorganic hybrid material and the substrate for a period of timesufficient to form a uniform melt;

laminating a protective layer of a material on the uniform melt toproduce a composite structure; and

cooling the composite structure to an ambient temperature underconditions sufficient to produce the laminated melt-processedorganic-inorganic hybrid material.

Additionally, the present invention provides the following processes forpreparing a melt-processed organic-inorganic hybrid material:

(1) a process for preparing a melt-processed organic-inorganic hybridmaterial including the steps of:

melt-spinning an organic-inorganic hybrid material onto a substrate; and

cooling the substrate and/or uniform melt to an ambient temperatureunder conditions sufficient to form the melt-processed organic-inorganichybrid material;

(2) a process for preparing a melt-processed organic-inorganic hybridmaterial including the steps of:

melt-dipping a substrate into a uniform melt of an organic-inorganichybrid material to produce a melt-dipped substrate; and

cooling the melt-dipped substrate to an ambient temperature underconditions sufficient to form the melt-processed organic-inorganichybrid material;

(3) a process for preparing a melt-processed organic-inorganic hybridmaterial including the steps of:

extruding an organic-inorganic hybrid material through a heatedextruder; and

cooling to an ambient temperature under conditions sufficient to formthe melt-processed organic-inorganic hybrid material; and

(4) a process for preparing a melt-processed organic-inorganic hybridmaterial including the steps of:

capillary-filling a uniform organic-inorganic hybrid material melt intoa narrow space capable of capillary action with or without the use ofvacuum; and

cooling to an ambient temperature under conditions sufficient to formthe melt-processed organic-inorganic hybrid material.

The present invention still further provides a method of preparing animproved field-effect transistor of the type having a source region anda drain region, a channel layer extending between the source region andthe drain region, the channel layer including a semiconductingorganic-inorganic hybrid material, a gate region disposed in spacedadjacency to the channel layer, an electrically insulating layer betweenthe gate region and the source region, drain region and channel layer.The improvement includes:

preparing a channel layer including a melt-processed semiconductingorganic-inorganic hybrid material by a process including the steps of:

maintaining an organic-inorganic hybrid material at a temperature abovethe melting point but below the decomposition temperature of theorganic-inorganic hybrid material for a period of time sufficient toform a uniform melt; and

cooling the uniform melt to an ambient temperature under conditionssufficient to produce the melt-processed organic-inorganic hybridmaterial.

The present invention provides low-cost, melt-processedorganic-inorganic hybrid materials, which have the advantages of beinglow cost. In addition, because they are fabricated without the use of asolvent, they are less of a hazard to the environment. Melt-processingcan be adapted to roll-to-roll manufacturing processes. Melt-processingalso allows control of the grain size of the organic-inorganic hybridmaterials. Further, melt-processing allows the preparation of alaminated layer between two substrate layers and as a result, the hybridlayer can be protected from the environment.

The low-cost, melt-processed organic-inorganic hybrid materialsaccording to the present invention can be used in a variety ofapplications, including flat panel displays, non-linearoptical/photoconductive devices, chemical sensors, emitting and chargetransporting layers in organic-inorganic light-emitting diodes,organic-inorganic thin-film transistors and as channel layers inorganic-inorganic field-effect transistors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of single-layer perovskites with:(a) monoammonium (RNH₃ ⁺) or (b) diammonium (⁺H₃NRNH₃ ⁺) organiccations. M is typically a divalent metal cation and X is a halide (F⁻,Cl⁻, Br⁻or I⁻).

FIG. 2 is a schematic representation of the <100>-oriented family oflayered organic-inorganic perovskites, (RNH₃)₂A_(y−1)M_(y)X_(3y+1),where R is an organic group, A⁺ is a small organic cation (e.g.methylammonium), M is generally a divalent metal cation, X is a halide(e.g., F⁻, Cl⁻, Br⁻, or I⁻), and y defines the thickness of theinorganic layers.

FIG. 3 shows differential scanning calorimetry (solid line) andthermogravimetric analysis (dashed line) plots for (C₆H₁₃NH₃)₂SnI₄.Exothermal transitions are up along the heat flow axis. M is the samplemass and T is the sample temperature. Scans were performed in a nitrogenatmosphere using a ramp rate of 5° C./min.

FIG. 4 shows differential scanning calorimetry scans for: (a)(3-FPEA)₂SnI₄, (b) PEA₂SnI₄, and (c) (2-FPEA)₂SnI₄. Scans were performedin a nitrogen atmosphere using a ramp rate of 5° C./min. Exothermaltransitions are up along the heat flow axis. In each scan, the * symbolmarks the melting transition peak.

FIG. 5 shows lattice spacing (d-spacing) for the (10 0 0) peak of(2-FPEA)₂SnI₄ as a function of temperature, clearly demonstrating thestructural transition at 175° C. The diffraction pattern disappearsabove 200° C. as the sample melts. Data were taken from high temperatureX-ray diffraction scans.

FIG. 6 shows differential scanning calorimetry scan for (4-FPEA)₂SnI₄.Scans were performed in a nitrogen atmosphere using a ramp rate of 5°C./min. Exothermal transitions are up along the heat flow axis. The *symbol marks the melting transition.

FIG. 7 shows room temperature crystal structure of: (a) (3-FPEA)₂SnI₄and (b) (2-FPEA)₂SnI₄, viewed down the b-axis. Dashed lines depict theunit cell outline.

FIG. 8 shows two hydrogen-bonding schemes typically encountered in the(RNH₃)₂MX₄ and (H₃NRNH₃)MX₄ type structures: (a) the bridging halideconfiguration and (b) the terminal halide configuration.

FIG. 9 shows room temperature X-ray diffraction patterns for (a) bulkcrystals of (2-FPEA)₂SnI₄ laying flat on a glass slide, (b) a deposit of(2-FPEA)₂SnI₄ formed on a glass slide by melting crystals of the hybridon the slide followed by cooling, and (c) a film formed by dipping aKapton sheet into a melt of (2-FPEA)₂SnI₄ and removing it to a roomtemperature environment. In (a), the indices of the reflections areindicated in parentheses.

FIG. 10 shows room temperature X-ray diffraction patterns for: (a) amelt-processed film of (2-FPEA)₂SnI₄ on a Kapton sheet, and the samefilm exposed to air for (b) 12 hours and (c) 24 hours. In pattern (a),the indices of the reflections are indicated in parentheses. The *symbol indicates the location of impurity peaks that develop duringexposure to air.

FIG. 11 shows room temperature X-ray diffraction patterns for: (a) amelt-processed film of (2-FPEA)₂SnI₄ laminated between two Kaptonsheets, and the same film exposed to air for (b) 12 hours and (c) 24hours. In (a), the indices of the reflections are indicated inparentheses. The * symbol indicates the location of impurity peaks thatdevelop during exposure to air.

DETAILED DESCRIPTION OF THE INVENTION

Organic-inorganic hybrid materials are a distinct class of materialswhich enable the combining of the useful characteristics of organic andinorganic components within a single material. Some members of thisclass of materials exhibit semiconducting characteristics. For thepurposes of this description, an organic-inorganic hybrid material is amaterial composed of organic components and inorganic components whichare mixed together on a molecular level, and (i) wherein the material ischaracterized by a substantially fixed ratio of each organic componentto each inorganic component; and (ii) wherein both organic and inorganiccomponents manifest forces that enable a self assembly therebetween intoa predictable arrangement.

One example of an organic-inorganic hybrid material takes the form of anorganic-inorganic perovskite structure. Layered perovskites maynaturally form a quantum well structure in which a two dimensionalsemiconductor layer of corner sharing metal halide octahedra and anorganic layer are alternately stacked.

For preparation of such organic-inorganic hybrid materials, spin coatingtechniques are often suitable because many organic-inorganic perovskitesare soluble in conventional aqueous or organic solvents. Using thismethod, high quality, highly oriented layered perovskite thin films havebeen achieved. Vacuum evaporation techniques have also been used to growfilms of layered perovskites. The commonly assigned U.S. Pat. Nos.6,117,498 and 5,871,579 describe alternative deposition methods fororganic-inorganic hybrid materials. The disclosure of the aforementionedis incorporated herein by reference. However, none of the methodsdescribed in the prior art teach the preparation of melt-processedorganic-inorganic hybrid material, including melt-processedorganic-inorganic perovskites.

Despite the convenience of solution-processing, potential problems withsolubility, surface wetting, and chemical incompatibility between thesolvent and hybrid limit the application of these techniques. It istherefore essential to consider other possibilities for film processing,with a special emphasis on those techniques that are compatible with arange of substrate materials and shapes (of particular interest areflexible plastic substrates).

Melt processing has proven very useful for the processing of selectedpolymeric organic and inorganic materials and provides a naturalopportunity to employ roll-to-roll, lamination, capillary filling, andextrusion techniques. For example, a new melt-spinnabledipentylamine-modified polyborazylene precursor to boron nitride ceramicfibers has recently been described (T. Wideman, et. al., Chem. Mater. 8,3 (1996)). Melt-processing of linear polyethylenes into films has beendescribed (using techniques including extrusion) in U.S. Pat. No.6,107,454.

In U.S. Pat. No. 4,829,116, a polyolefin molding composition isdescribed with improved extrusion throughput. Japanese Patent DocumentJP 2000-202,906 describes a process in which molten polymers, includingPET, are melt-extruded through a T-die onto a roll whose surface wasbead blasted, Cr-coated, and subject to a voltage, to obtain a moldingvelocity of 84 m/min. In addition, utilization of a melt enablescapillary filling between two closely placed substrates, as done inliquid crystal display manufacturing.

Gradual heating of organic-inorganic hybrids might be expected todecompose or dissociate the organic component at a lower temperaturethan that required for melting. In the metal-halide-based perovskitefamily (C₄H₉NH₃)₂MI₄ (M=Pb, Sn, and Ge), however, the meltingtemperature progressively decreases across the series from Pb to Ge suchthat, while both the M=Sn and Pb compounds decompose before or duringmelting (as is typical for the hybrids), the M=Ge compound forms areasonably stable melt phase (T_(m)=222° C.).

The present invention provides a process for producing melt-processedorganic-inorganic hybrid materials, preferably in the form of a film, asheet, a thick section, an extrudate or a fiber, using low-temperaturemelt-processing techniques. The process includes the steps of:

maintaining an organic-inorganic hybrid material at a temperature abovethe melting point but below the decomposition temperature of theorganic-inorganic hybrid material for a period of time sufficient toform a uniform melt; and

cooling the uniform melt to an ambient temperature under conditionssufficient to produce the melt-processed organic-inorganic hybridmaterial.

A melt-processed organic-inorganic hybrid material film according to thepresent invention can be a single crystal of the organic-inorganichybrid material. Preferably, the melt-processed organic-inorganic hybridmaterial is a polycrystalline material having a grain size equal to orgreater than the dimensions between contacts in a device, such as, asemiconductor device, in which it is to be used.

One of the requirements of the solid organic-inorganic hybrid materialis that it should preferably have a melting point that is below itsdecomposition temperature, so that it can melt during processing withoutsignificant decomposition.

To examine the influence of the organic cation on the thermal propertiesof isostructural tin(II) iodide based hybrids, (R—NH₃)₂SnI₄, severalrelated phenethylammonium-based cations were considered, including, forexample, phenethylammonium (PEA), 2-fluorophenethylammonium (2-FPEA),3-fluorophenethylammonium (3-FPEA), and2,3,4,5,6-pentafluorophenethylammonium (5FPEA). The four perovskiteswere prepared as previously reported (Mitzi., D. B.; Dimitrakopoulos, C.D.; Kosbar, L. L. Chem. Mater. 2001, 13, 3728).

Each member of the phenethylammonium-based family, (R—NH₃)₂SnI₄, whereR—NH₃ ⁺=2,3,4,5,6-pentafluorophenethylammonium (5FPEA),3-fluorophenethylammonium (3-FPEA), phenethylammonium (PEA), and2-fluorophenethylammonium (2-FPEA), was studied using thermal analysisand temperature-programmed powder X-ray diffraction. The meltingtemperature decreases across the cation series: 253(1)° C. (with partialdecomposition) [(5FPEA)₂SnI₄], 233.0(8)° C. [(3-FPEA)₂SnI₄], 213.4(8)°C. [(PEA)₂SnI₄], and 200.8(8)° C. [(2-FPEA)₂SnI₄], while the bulkdecomposition temperatures of the hybrids remain relatively fixed tovalues between 255-261° C. While the (5FPEA)₂SnI₄ sample decomposes asit melts, the melt becomes significantly more stable as the temperatureof melting transition, T_(b), decreases across the cation series.Notably, the temperatures of melting and structural transitions duringthermal analysis are reproducible with respect to different heatingrates, sample size and morphology (crystal versus powder). In contrast,the decomposition temperature depends on how easy it is for the organicmaterial to diffuse from the sample (i.e. for crystals the transition isgenerally at a higher temperature than for powders).

Before melting, a first-order structural transition is observed,corresponding to a substantial increase in the crystallographicseparation between adjacent tin(II) iodide layers. The temperature ofthis transition tracks approximately 24(3)° C. below the bulk meltingpoint.

The ability to form a stable melt at low temperatures (˜200° C.)provides an ideal opportunity to process films of the semiconductinghybrids from the melt on organic-based substrates. Highly crystallineand oriented melt-processed films of the tin(II)-iodide-basedperovskites have been prepared on Kapton sheets, providing a convenientpathway for the fabrication of electronic devices (e.g., TFTs and LEDs)on flexible substrates. The ability to laminate the hybridsemiconductors between sheets of plastic may also serve to protect theair-sensitive materials from environmental factors.

The melt-processed organic-inorganic perovskites described above combinethe advantages of an inorganic, crystalline semiconductor with those ofan organic material. The inorganic component forms an extended,inorganic one-, two-, or three-dimensional network to potentiallyprovide the high carrier mobilities characteristic of inorganic,crystalline solids. The organic component facilitates the self-assemblyof these materials. This enables the materials to be applied by simplemelt-processing techniques such as those described above. The organiccomponent is also used to tailor the electronic properties of theinorganic framework by defining the dimensionality of the inorganiccomponent and the electronic coupling between inorganic units. Thus, theelectronic properties of organic-inorganic hybrid materials may betailored through chemistry. There is a wide-range of organic andinorganic components usable as the organic-inorganic hybrid material.

The solid organic-inorganic hybrid material should preferably have amelting point that is below its decomposition temperature, so that itcan melt during processing without significant decomposition. Also, oneor both of the organic and inorganic components of the solidorganic-inorganic hybrid material may preferably be semiconducting.Accordingly, materials with desired properties can be designed, forexample, by choosing a particular chemistry, crystal structure, anddimensionality of the inorganic component and the length and chemicalfunctionality of the organic component.

The flexibility in the chemistry of organic-inorganic hybrid materialsmay be used to prepare both n- and p-type transporting materials, whichare desirable, for example, for application in complementary logic andnormally on- or off-TFTs.

Suitable organic-inorganic hybrid materials include an inorganic anionlayer having a metal-ligand framework and an organic cation layer havingan organic cation capable of templating the metal-ligand inorganic anionlayers within the organic-inorganic hybrid material structure. Themetal-ligand framework includes a metal ligand pair, such as,corner-sharing metal ligand octahedra, corner-sharing metal ligandtetrahedra, corner-sharing metal ligand trigonal bipyramids,face-sharing metal ligand octahedra, face-sharing metal ligandtetrahedra, face-sharing metal ligand trigonal bipyramids, edge-sharingmetal ligand octahedra, edge-sharing metal ligand tetrahedra oredge-sharing metal ligand trigonal bipyramids. The metal ligand pair canbe a metal halide, a metal oxide or a metal sulfide.

Preferably, the organic-inorganic hybrid material is anorganic-inorganic perovskite. Perovskites are a subclass of the abovedescribed organic-inorganic hybrid materials. They include alternatinglayers of an inorganic anion layer having a metal halide framework ofcorner-sharing metal halide octahedra and an organic cation layer havinga plurality of organic cations capable of templating the metal halideinorganic anion layers within the perovskite structure. The metal has avalence n in the range of from 2 to 6, the metal halide layer beingrepresented by the formula:(M^(n+))_(2/n)V_((n−2)/n)X₄ ²⁻wherein M is a metal; V is a vacancy; X is a halide; and n is an integerin the range of from 2 to 6.

Preferred metals include Sn²⁺, Pb²⁺, Ge²⁺, Cu²⁺, Ni²⁺, Co²⁺, Fe²⁺, Mn²⁺,Cr²⁺, V²⁺, Pd²⁺, Cd²⁺, Pt²⁺, Rh²⁺, Eu²⁺, Yb²⁺, Sm²⁺, Bi³⁺, Sb³⁺, In³⁺,Sn⁴⁺, Te⁴⁺, Hf⁴⁺, Nb⁵⁺, Ta⁵⁺, Mo⁵⁺ and a combination thereof. Morepreferred metals include Sn²⁺, Pb²⁺, Bi³⁺, Sb³⁺, Te⁴⁺ and a combinationthereof.

The halide in the metal salt used to prepare the organic-inorganicperovskite of the present invention can be fluoride, chloride, bromide,iodide, or a combination thereof. The preferred halide is iodide.Examples of the trivalent metal iodides include, for example,bismuth(III) iodide, antimony(III) iodide and mixtures thereof.

In order to stabilize the layered perovskite framework with the highervalent metals, it is also necessary to chose an organic counter-cationthat will facilitate or template the formation of the characteristicinorganic layers of corner-sharing metal halide octahedra within theperovskite structures. The preferred organic cations include an organicmono-ammonium cation, an organic diammonium cation and a combinationthereof.

Accordingly, the perovskite materials of the present invention employ anorganic cation, such as an organic diammonium cation, as the organiccounter-cation to template and facilitate the formation of thecharacteristic inorganic anion layers of corner-sharing metal halideoctahedra within the perovskite structures. The perovskites willself-assemble by introducing vacancies on the metal site in the correctquantity to counterbalance the larger charge on the metal site. Thus,using such organic diammonium cations produces an organic-inorganicperovskite structure with alternating inorganic anion and organic cationlayers.

The organic diammonium cation can be any dication derived from ahydrogen halide and an organic diamine to produce a diammonium salt,such as an organic diammonium dihalide. The organic cation must have anappropriate size and shape to fit within the layered perovskiteframework and have intermolecular interactions that favor the formationof the organic-inorganic layered perovskite structures. Preferably, theorganic diammonium cation has 2 to 60 carbon atoms, more preferably 6 to60 carbon atoms, most preferably 10 to 30 carbon atoms.

Preferred examples of such organic di-ammonium cations include1,2-ethylene diamine, 1,3-propylene diamine, 1,4-butylene diamine,bis-(aminoalkyl)-substituted arylene, bis-(aminoalkyl)-substitutedheteroarylene and a combination thereof. Preferably, the diamine has astring of 2-6 aromatic moieties each of which can independently be aphenylene, naphthylene, anthracene, phenanthrene, furan or thiophene. Anexamples of such organic diammonium cation is obtained by protonation of5,5′″-bis(aminoethyl)-2,2′:5′,2″:5″,2′″-quaterthiophene (AEQT).

Preferred examples of such organic mono-ammonium cations includephenethylammonium, 2-fluorophenethylammonium, 2-chlorophenethylammonium,2-bromophenethylammonium, 3-fluorophenethylammonium,3-chlorophenethylammonium, 3-bromophenethylammonium,4-fluorophenethylammonium, 4-chlorophenethylammonium,4-bromophenethylammonium, 2,3,4,5,6-pentafluorophenethylammonium and acombination thereof.

In a preferred embodiment of the invention, the process includes thesteps of applying the solid organic-inorganic hybrid material onto asubstrate having a melting and decomposition point above the meltingpoint of the organic-inorganic hybrid material.

Preferably, the substrate is fabricated from a material having at leastone property selected from the following: thermally inert, chemicallyinert, rigid or flexible. Suitable examples include Kapton, silicon,amorphous hydrogenated silicon, silicon carbide (SiC), silicon dioxide(SiO₂), quartz, sapphire, glass, diamond-like carbon, hydrogenateddiamond-like carbon, gallium nitride, gallium arsenide, germanium,silicon-germanium, indium tin oxide, boron carbide, boron nitride,silicon nitride (Si₃N₄), alumina (Al₂O₃), cerium(IV) oxide (CeO₂), tinoxide (SnO₂), zinc titanate (ZnTiO₂), a plastic material and acombination thereof. Preferably, the plastic material is polycarbonate,Mylar or Kevlar.

Preferably, the organic-inorganic hybrid material has a melting pointbelow the melting point or decomposition temperature of the substrate,so that the organic-inorganic hybrid material melts before the substratemelts or decomposes.

Films can be prepared by melting the organic-inorganic hybrid material,for example, on a suitable substrate or container, such as, a crucible,and either allowing the melt to freely flow on the substrate or byconfining the melt between the substrate and an overlayer sheet of achemically and thermally inert material or between two sheets of theinert material, followed by a cooling step.

In the practice of the process of the present invention, the coolingstep, which produces the melt-processed organic-inorganic hybridmaterial, is critical. Preferably, cooling to an ambient temperature iscarried out at a rate from about 0.001° C./sec to about 1000° C./sec,preferably by exposing the uniform melt to a temperature gradient forcontrolling the grain size of the melt-processed organic-inorganichybrid material. Thus, with slow cooling under the proper coolingconditions, a single crystal film of the melt-processedorganic-inorganic hybrid material can be produced, i.e., amelt-processed organic-inorganic hybrid material film including a singlecrystal of the organic-inorganic hybrid material. Thus, for example, themelt-processed organic-inorganic hybrid material can be apolycrystalline material preferably having a grain size equal to orgreater than the dimensions between contacts in a semiconductor device.

In another embodiment, a melt-processed organic-inorganic hybridmaterial can be prepared by a process including the steps of:

applying onto a substrate an organic-inorganic hybrid material;

maintaining the substrate and/or the organic-inorganic hybrid materialat a temperature above the melting point of the organic-inorganic hybridmaterial but below the decomposition temperature of theorganic-inorganic hybrid material and the substrate for a period of timesufficient to form a uniform melt; and

cooling the substrate and/or uniform melt to an ambient temperatureunder conditions sufficient to form the melt-processed organic-inorganichybrid material.

The process can further include heating the substrate prior to applyingthe organic-inorganic hybrid material onto the substrate to atemperature above the melting point of the organic-inorganic hybridmaterial and/or heating the substrate and the solid organic-inorganichybrid material to a temperature above the melting point of theorganic-inorganic hybrid material but below the decompositiontemperature of the organic-inorganic hybrid material and the substrate.In such cases, the organic-inorganic hybrid material preferably has amelting point below the melting point or decomposition temperature ofthe substrate. However, in all cases, the organic-inorganic hybridmaterial has a melting point which is below its decompositiontemperature.

In another preferred embodiment of the invention, a laminatedmelt-processed organic-inorganic hybrid material can be prepared by aprocess, which includes the steps of:

applying onto a substrate an organic-inorganic hybrid material;

maintaining the substrate and/or the organic-inorganic hybrid materialat a temperature above the melting point of the organic-inorganic hybridmaterial but below the decomposition temperature of theorganic-inorganic hybrid material and the substrate for a period of timesufficient to form a uniform melt;

laminating a protective layer of a material on the uniform melt toproduce a composite structure; and

cooling the composite structure to an ambient temperature underconditions sufficient to produce the laminated melt-processedorganic-inorganic hybrid material.

Preferably, the laminated protective layer and the substrate arefabricated from the same material. However, they can also be fabricatedfrom different materials. In the case of lamination between sheets of aninert material, the outer sheets can also serve to protect theorganic-inorganic hybrid from attack by air or moisture or otherchemical contaminants.

Melt-processing can be achieved by a number of approaches known in theart. Accordingly, the present invention provides a process for preparingsuch melt-processed organic-inorganic hybrid materials including thesteps of:

(1) melt-spinning an organic-inorganic hybrid material onto a substrateand cooling the substrate and/or uniform melt to an ambient temperatureunder conditions sufficient to form the melt-processed organic-inorganichybrid material;

(2) melt-dipping a substrate into a uniform melt of an organic-inorganichybrid material to produce a melt-dipped substrate and cooling themelt-dipped substrate to an ambient temperature under conditionssufficient to form the melt-processed organic-inorganic hybrid material;

(3) extruding an organic-inorganic hybrid material through a heatedextruder and cooling to an ambient temperature under conditionssufficient to form the melt-processed organic-inorganic hybrid material;or

(4) capillary-filling a uniform organic-inorganic hybrid material meltinto a narrow space capable of capillary action, with or without the useof vacuum, and cooling to an ambient temperature under conditionssufficient to form the melt-processed organic-inorganic hybrid material.

In the case of the capillary-filling process, the narrow space that iscapable of capillary action can be, for example, a capillary tube or anarrow space between two rigid or flexible substrates.

In an example of melt processing, the organic-inorganic films are formedin a nitrogen-filled glovebox by heating (on a temperature-controlledhotplate) an 8 μm thick Kapton sheet approximately 10° C. above theexpected melting temperature of the hybrid, placing hybrid crystals orpowder on the sheet, and immediately depositing another Kapton sheet ontop of the melting materials. The hybrid melt effectively wets theKapton and capillary action spreads the melt uniformly between thesheets, leading to the formation of a film, the thickness of whichdepends on the initial quantity of hybrid (generally in the range 0.5-10μm). Thinner hybrid films can be achieved by application of pressure tothe top Kapton sheet during the melt process.

After allowing the film to spread, it is cooled below the meltingtemperature, resulting in a polycrystalline film laminated between thetwo Kapton sheets. The x-ray diffraction pattern for the (5FPEA)₂SnI₄example indicates substantial decomposition during the melting process,while the (3-FPEA)₂SnI₄ sample has a slightly shifted spacing betweenthe inorganic sheets relative to the bulk solution-grown crystals (16.63Å vs. 16.79 Å), presumeably due to the proximity of the melting anddecomposition transitions.

The diffraction patterns for the two lower melting point films based on(PEA)₂SnI₄ and (2-FPEA)₂SnI₄ are identical with the initial crystals andthe large number of higher order (h 0 0) reflections attest to thepreferred orientation and high degree of crystallinity of the films. Theresulting Kapton/hybrid/Kapton laminate is flexible and the Kaptonsheets serve to partially protect the hybrid materials from theenvironment (as evidenced by repeated X-ray diffraction scans of thefilms in air). A higher degree of protection may be afforded by usingKapton sheets coated with a gas/moisture impermeable membrane.

As described above, the organic-inorganic hybrid material is preferablyselected from members of the organic-inorganic perovskite family. Suchorganic-inorganic perovskites include inorganic sheets of corner-sharingmetal halide octahedra, alternating with bilayers of organicmonoammonium cations or monolayers of diammonium cations (see FIG. 1).The influence of the organic cation on the melting properties may derivefrom changes in the specific hydrogen bonding interactions between thecation and the inorganic component of the structure, from differentpacking interactions (e.g., aromatic-aromatic interactions) among theorganic cations, or more indirectly from subtle changes in the structureof the inorganic framework induced by the different cations.

Referring to FIG. 1, structures (a) and (b), a schematic representationof single-layer perovskites with: (a) monoammonium (RNH₃ ⁺) and (b)diammonium (⁺H₃NRNH₃ ⁺) organic cations are shown. M is typically adivalent metal cation and X is a halide (F⁻, Cl⁻, Br⁻ or I⁻).

The metal halide sheets typically include divalent metals, includingCu²⁺, Mn²⁺, Fe²⁺, Ni²⁺, Cd²⁺, Cr⁺, Sn²⁺, Ge²⁺, and Pb²⁺, and halideions, including Cl⁻, Br⁻, and I⁻. Recently trivalent metals, includingBi³⁺ and Sb³⁺, have also been incorporated within the layered perovskiteframework through the appropriate choice of organic cation, whichtemplates the formation of metal-deficient inorganic sheets (D. B.Mitzi, J. Chem. Soc., Dalton Trans., 1 (2001)). Single and multipleinorganic layers can be sandwiched between the organic cation layers(enabling control over the effective dimensionality of the inorganicframework) (FIG. 2).

FIG. 2 is a schematic representation of the <100>-oriented family oflayered organic-inorganic perovskites, (RNH₃)₂A_(y−1)M_(y)X_(3y+1),where R is an organic group, A⁺ is a small organic cation (e.g.methylammonium), M is generally a divalent metal cation, X is a halide(e.g., Cl⁻, Br⁻, I⁻), and y defines the thickness of the inorganiclayers.

These structures are conceptually derived from the three-dimensionalcubic perovskite structure by taking y-layer-thick cuts from thethree-dimensional structure along the <100> crystallographic directionand stacking these layers in alternation with organic cation bilayers.The crystallographic orientation of the inorganic sheets can also becontrolled, e.g., <110>- or <111>-oriented inorganic layers versus the<100>-oriented layers in FIG. 2, through the appropriate choice oforganic cation (D. B. Mitzi, J. Chem. Soc., Dalton Trans., 1 (2001)).

One particularly interesting family of layered organic-inorganicperovskites is based on tin(II) iodide sheets. In contrast to most metalhalides, which are insulating, the tin(II) iodide based perovskitesexhibit semiconducting and even metallic character.

The family (C₄H₉NH₃)₂(CH₃NH₃)_(y−1)Sn_(y)I_(3y+1), for example, exhibitsa semiconductor-metal transition as a function of increasing thicknessof the perovskite sheets (controlled by y) (D. B. Mitzi, et. al., Nature369, 467 (1994)). The Hall effect mobility for pressed pellet samples ofthe cubic perovskite CH₃NH₃SnI₃ is ˜50 cm²N-sec (D. B. Mitzi, et. al.,J. Solid State Chem. 114, 159 (1995)). Given appropriate thin filmdeposition techniques, these alternative semiconductors thereforepresent important opportunities with respect to semiconductor deviceapplications. Spin-coated thin films of (C₆H₅C₂H₄NH₃)₂SnI₄ and relatedsemiconducting hybrid perovskites, for example, exhibit field-effectmobilities and on-off ratios of ˜1 cm²N-sec and >10⁵, respectively,comparable to the values achieved for amorphous silicon (C. R. Kagan,et. al., Science 286, 945 (1999)).

While melt processing is useful for selected organic materials, gradualheating of organic-inorganic hybrids is generally expected to lead tothe decomposition or dissociation of the organic component at a lowertemperature than that required for melting the hybrid (M. J. Tello, et.al., Thermochim. Acta 11, 96 (1975)), thereby inhibiting the ability toprocess these materials using melting techniques. The hybrid perovskite(C₄H₉NH₃)₂GeI₄ melts at 222° C., as one of the only previously knownexamples of hybrid perovskites that melt before decomposition. However,the corresponding Sn(II) analog, (C₄H₉NH₃)₂SnI₄, melts and decomposes atapproximately the same temperature (D. B. Mitzi, Chem. Mater., 8, 791(1996)).

FIG. 3 shows differential scanning dalorimetry (solid line) andthermogravimetric analysis (dashed line) plots for (C₆H₁₃NH₃)₂SnI₄.Exothermal transitions are up along the heat flow axis. M is the samplemass and T is the sample temperature. Scans were performed in a nitrogenatmosphere using a ramp rate of 5° C./min.

The thermal analysis of the layered perovskite (C₆H₁₃NH₃)₂SnI₄ (FIG. 3)indicates that the hybrid decomposes or dissociates at a lowertemperature than that required for melting. This is evident both by thelarge exotherm at ˜225° C. and the corresponding weight loss, whichcorrelates with this transition (i.e., see dM/dT plot). No organiccation-dependence to the melting properties has been previously notedand, in particular, it has not been possible to melt-process the usefulclass of tin(II) iodide based organic-inorganic perovskites.

FIG. 4 shows differential scanning calorimetry scans for: (a)(3-FPEA)₂SnI₄, (b) PEA₂SnI₄, and (c) (2-FPEA)₂SnI₄. Scans were performedin a nitrogen atmosphere using a ramp rate of 5° C./min. Exothermaltransitions are up along the heat flow axis. In each scan, the * symbolmarks the melting transition peak.

In FIG. 4, the differential scanning calorimetry (DSC) scan for the(3-FPEA)₂SnI₄ layered perovskite (where 3FPEA=3-fluorophenethylammonium)is shown (a). The first endotherm at 207° C. corresponds to a structuraltransition. The second endotherm, which merges with the decompositionexotherm at ˜225° C., corresponds to the onset of melting. The nature ofeach of these transitions has been verified using temperature-dependentX-ray scans.

Despite the fact that both the (C₆H₁₃NH₃)₂SnI₄ and the (3-FPEA)₂SnI₄structures consist of very similar inorganic sheets of corner-sharingSnI₆ octahedra, the thermal behavior (i.e. melting and decompositionproperties) are substantially different. In particular, the meltingtransition in (3-FPEA)₂SnI₄ is shifted slightly below the decompositionpoint of the hybrid. Since the organic cation constitutes the majordifference between these two structures, this indicates that the organiccation can be used to control the melting properties of the hybrid. Thiscontrol derives from the fact that organic cations with different shapeand functionality will hydrogen bond to the inorganic framework in adifferent fashion. Changes in hydrogen bonding between the organiccation and the inorganic layers and in interactions among the organicmolecules themselves will, in turn, provide a degree of control over howthe material melts or decomposes as a function of temperature.

Based on this, it is possible to tailor the organic cation in such a wayso as to reduce the melting temperature. In particular, it is desirableto reduce the melting temperature further below the decompositiontemperature of the hybrid material, as well as below that for potentialorganic-based flexible substrates, to enable melt processing. FIG. 4,(b) and (c) show the DSC scans for (PEA)₂SnI₄ and (2-FPEA)₂SnI₄, wherePEA=phenethylammonium and 2-FPEA=2-fluorophenethylammonium. Thesecompounds are very similar to the (3-FPEA)₂SnI₄ compound, except thatfor the PEA system, the fluorine atom has been removed from thesubstituted phenethylammonium cation and the 2-FPEA system has thefluorine substitution at a different site on the phenethylammoniumcation.

It should be noted that the 3-FPEA and 2-FPEA systems are in factisostructural (i.e. same space group and cell). Clearly evident in thisprogression is that the melting temperature shifts to lower temperatureand, most significantly, in (2-FPEA)₂SnI₄ the melting temperature isreduced substantially below the decomposition temperature.

FIG. 5 shows lattice spacing (d-spacing) for the (10 0 0) peak of(2-FPEA)₂SnI₄ as a function of temperature, clearly demonstrating thestructural transition at 175° C. The diffraction pattern disappearsabove 200° C. as the sample melts. Data were taken from high temperatureX-ray diffraction scans. In FIG. 5, the (10 0 0) diffraction X-raydiffraction peak for (2-FPEA)₂SnI₄ as a function of temperature clearlyindicates the structural and melting transitions. The meltingtemperature of 199° C. is low enough to enable melt processing onflexible plastic substrates such as Kapton.

The corresponding 4-FPEA (4-fluorophenethylammonium) system has a verysimilar crystallographic cell (although it is not isostructural). Thethermal analysis plots for (4-FPEA)₂SnI₄ are shown in FIG. 6, i.e., thedifferential scanning calorimetry scan for (4-FPEA)₂SnI₄. Scans wereperformed in a nitrogen atmosphere using a ramp rate of 5° C./min.Exothermal transitions are up along the heat flow axis. The * symbolmarks the melting transition.

In this case, there is no low-temperature structural transition evident.As for the 2-FPEA analog, however, the material melts before itdecomposes (although the melting temperature is substantially above thatfor the 2-FPEA system).

Despite the minor changes to the organic cation in each of thesesystems, the effect on the thermal properties is important and providesan opportunity for tailoring the thermal properties of the material toenable melt processing. In essence, the organic-inorganic perovskitesprovide the opportunity to combine the mobility characteristics of theinorganic framework with the structure-directing (and therefore thermalproperty directing) influence of the organic cation component of thestructure. The SnI₂ (without the organic cation) melts at 320° C.

FIG. 7 shows room temperature crystal structure of: (a) (3-FPEA)₂SnI₄and (b) (2-FPEA)₂SnI₄, viewed down the b-axis. Dashed lines depict theunit cell outline. In evaluating the potential impact of the organiccation on the crystal structure, the (2-FPEA)₂SnI₄ and (3-FPEA)₂SnI₄structures can be used as an example (FIG. 7, structures (a) and (b))since these two hybrids are isostructural despite the substantiallydifferent thermal properties.

At room temperature, the (3-FPEA)₂SnI₄ structure adopts a monoclinic(C2/c) structure, with the lattice parameters, a=34.593(4) Å,b=6.0990(8) Å, c=12.254(2) Å, and β=103.917(2)°. The structure consistsof two-dimensional sheets of tin(II) iodide octahedra, alternating withbilayers of the 3-FPEA cations. The average tin(II)-iodine bondingdistance is 3.160 Å and the average Sn—I—Sn bond angle is 154.2°,indicating that adjacent SnI₆ octahedra are substantially tiltedrelative to each other. The isostructural (2-FPEA)₂SnI₄ structure adoptsa monoclinic (C2/c) structure, with the lattice parameters, a=35.070(3)Å, b=6.1165(5) Å, c=12.280(1) Å, and β=108.175(1)°. The average Sn—Ibond length is 3.159 Å, virtually identical to that found in(3-FPEA)₂SnI₄, and the average Sn—I—Sn bond angle is 153.3°, slightlysmaller than for the (3-FPEA)₂SnI₄ structure. Given the similarinorganic frameworks and related organic cations, the different thermalproperties most likely arise from the differences in the interactionbetween the organic cation and the inorganic framework.

The choice of hydrogen bonding scheme is important for determining theorientation and conformation of the organic molecule within the layeredhybrid structure.

FIG. 8 shows two hydrogen-bonding schemes typically encountered in the(RNH₃)₂MX₄ and (H₃NRNH₃)MX₄ type structures: (a) the bridging halideconfiguration and (b) the terminal halide configuration.

In principle, the ammonium head(s) of the organic cations can hydrogenbond to any of the eight halides (i.e. four bridging/four terminal)within the holes formed by the corner-sharing MX₆ octahedra (FIG. 8,structures (a) and (b)).

In practice, due to the geometric constraints of the ammonium group andthe organic tail, the N—H . . . X interactions generally form eitherprimarily to two bridging halogens and one terminal halogen (bridginghalogen configuration) or to two terminal halogens and one bridginghalogen (terminal halogen configuration). For both the (3-FPEA)₂SnI₄ and(2-FPEA)₂SnI₄ structures, the phenethylammonium-based organic cationshydrogen bond using the terminal halogen configuration. However, for(3-FPEA)₂SnI₄, the average distance between the ammonium nitrogen andthe five closest iodides involved with hydrogen bonding is 3.71 Å (theother three iodides are significantly further away and are therefore notsignificantly involved with hydrogen bonding), whereas for(2-FPEA)₂SnI₄, the same distance is 3.77 Å.

The increased hydrogen bonding distance (which presumably correlateswith weaker hydrogen bonding) may arise because of the stericinteraction between the substituted fluorine and the apical iodides fromthe tin(II) iodide octahedra. In the (2-FPEA)₂SnI₄ system, there is aclose interaction between the fluorine and the apical iodide of 3.782(8)Å, whereas there are no close F . . . I interactions for the(3-FPEA)₂SnI₄ system. In this way, the choice of organic cation caninfluence the hydrogen bonding (among other structural factors), andtherefore the thermal properties of the solid.

Since the tailored hybrid perovskites can be heated to melting withoutdecomposition, melt-processed films become possible.

FIG. 9 shows room temperature X-ray diffraction patterns for (a) bulkcrystals of (2-FPEA)₂SnI₄ laying flat on a glass slide, (b) a deposit of(2-FPEA)₂SnI₄ formed on a glass slide by melting crystals of the hybridon the slide followed by cooling, and (c) a film formed by dipping aKapton sheet into a melt of (2-FPEA)₂SnI₄ and removing it to a roomtemperature environment. In pattern (a), the indices of the reflectionsare indicated in parentheses.

FIG. 9, pattern (b), shows the X-ray diffraction pattern for a depositthat was created by melting an array of (2-FPEA)₂SnI₄ crystals on aglass substrate at 205° C. and allowing the melt to freely flow beforecooling. Note that, as for the bulk crystals, only (2h 0 0) reflectionsare observed, indicating that the film is highly oriented with the planeof the perovskite sheets parallel to the glass substrate. The manyorders of reflection that are observed indicate the high degree ofcrystallinity of the deposits.

FIG. 9, pattern (c) shows the X-ray diffraction pattern for a Kaptonsheet, which has been dipped in a melt of the (2-FPEA)₂SnI₄ hybrid heldat 220° C. and immediately removed. Notice that, in each case, themelt-processed deposits are the same material and of similar crystallinequality as the bulk (2-FPEA)₂SnI₄ crystals (FIG. 9, pattern (a)).

FIG. 10 shows room temperature X-ray diffraction patterns for: (a) amelt-processed film of (2-FPEA)₂SnI₄ on a Kapton sheet, and the samefilm exposed to air for pattern (b) 12 hours and pattern (c) 24 hours.In pattern (a), the indices of the reflections are indicated inparentheses. The * symbol indicates the location of impurity peaks thatdevelop during exposure to air.

In FIG. 10, pattern (a), a film of (2-FPEA)₂SnI₄ was deposited on a thin(0.3 mil/8 μm) Kapton sheet by melting the hybrid on the sheet at 215°C. on a hot plate (in a nitrogen-filled drybox). The film was formed bydropping a second sheet of Kapton on top of the melt, which creates auniform layer of melt by capillary action, and then by removing thesecond sheet before cooling. As for the deposit formed on glass and thedipped film, the currently described film is highly crystalline andoriented.

FIG. 10, patterns (b) and (c) show the X-ray diffraction pattern for thesame film after 12 and 24 hours exposure to air, respectively. Thegrowth of impurity peaks and reduction in the intensity of the originalperovskite peaks attests to the air-sensitivity of the tin(II) iodidebased perovskites. Note that after 24 hrs, most of the film hasdecomposed.

FIG. 11, patterns (a), (b) and (c) show room temperature X-raydiffraction patterns for: (a) a melt-processed film of (2-FPEA)₂SnI₄laminated between two Kapton sheets, and the same film exposed to airfor (b) 12 hours and (c) 24 hours. In (a), the indices of thereflections are indicated in parentheses. The * symbol indicates thelocation of impurity peaks that develop during exposure to air.

As shown in FIG. 11, an X-ray diffraction experiment was performed for afilm of (2-FPEA)₂SnI₄ that was formed by leaving the second Kapton sheeton top of the melt and cooling the laminated melt by shutting off thehot plate. The Kapton/(2-FPEA)₂SnI₄/Kapton laminated hybrid filmexhibits the same diffraction pattern as the film with a Kapton sheet ononly one side. However, the 12 hr and 24 hr air exposure patterns forthe laminated film indicate that the film is significantly lesssusceptible to decomposition in air.

It should be noted that the sides of the laminated structure were notsealed in the current experiment. Therefore, it is expected that thedecomposition could be further slowed by sealing the sides of theKapton/(2-FPEA)₂SnI₄/Kapton assembly. In addition, a natural extensionof these results would be to use Kapton sheets that are coated with somebarrier material to prevent diffusion of air, moisture or otherdeleterious molecular species from reaching the sample. Finally, theKapton/(2-FPEA)₂SnI₄/Kapton assembly could be bent and flexed with noapparent degradation of the hybrid material (i.e., macroscopic cracksand delamination).

The melt-processing techniques, enabled by the tailoredorganic-inorganic hybrids, are not limited to the thin film depositiontechniques discussed in the embodiments presented above. As formelt-processable organic polymeric materials, the organic-inorganichybrids can also be processed using other thin film and fiber techniquesknow to the field, including melt spinning, extrusion and roll-to-rollprocessing. In addition, while the technique is demonstrated withorganic-inorganic perovskites, other organic-inorganic hybrids, withappropriately tailored organic and inorganic frameworks, could also beprocessed using the techniques described herein.

The present invention further provides a thin film field-effecttransistor (FET) having a melt-processed organic-inorganic hybridmaterial as the active semiconductor layer.

Field-effect transistors (FET) that use organic-inorganic hybridmaterials as the active semiconductor layer are well known in the art.For example, such field-effect transistors (FET) that useorganic-inorganic hybrid materials are described in the commonly ownedU.S. Pat. No. 6,180,956, the contents of which are incorporated hereinby reference. However, the organic-inorganic hybrid materials used inthis patent is not melt-processed organic-inorganic hybrid materials.

Accordingly, the present invention provides a method of preparing animproved field-effect transistor of the type having a source region anda drain region, a channel layer extending between the source region andthe drain region, the channel layer including a semiconductingorganic-inorganic hybrid material, a gate region disposed in spacedadjacency to the channel layer, an electrically insulating layer betweenthe gate region and the source region, drain region and channel layer,wherein the improvement includes:

preparing a channel layer including a melt-processed semiconductingorganic-inorganic hybrid material by a process including the steps of:

maintaining an organic-inorganic hybrid material at a temperature abovethe melting point but below the decomposition temperature of theorganic-inorganic hybrid material for a period of time sufficient toform a uniform melt; and

cooling the uniform melt to an ambient temperature under conditionssufficient to produce the melt-processed organic-inorganic hybridmaterial.

In one embodiment, the source region, channel layer and drain region arepreferably disposed upon a surface of a substrate, the electricallyinsulating layer is disposed over the channel layer and extending fromthe source region to the drain region, and the gate region is disposedover the electrically insulating layer, for example, as shown in FIG. 4of the previously incorporated U.S. Pat. No. 6,180,956.

In another embodiment, the gate region is disposed as a gate layer upona surface of a substrate, the electrically insulating layer is disposedupon the gate layer, and the source region, channel layer, and drainregion are disposed upon the electrically insulating layer, for example,as shown in FIG. 3 of the previously incorporated U.S. Pat. No.6,180,956.

Preferably, the melt-processed organic-inorganic hybrid material is inthe form of a film, i.e., an organic-inorganic hybrid material film inwhich the organic-inorganic hybrid material is a polycrystallinematerial having a grain size equal to or greater than the dimensionsbetween contacts in the semiconductor device. Accordingly, the presentinvention can provide an improved field-effect transistor prepared bythe aforementioned method.

The processes described herein are useful in creating semiconductorfilms for applications including, for example, thin-film transistors(TFTs) and light-emitting devices (LEDs).

The present invention has been described with particular reference tothe preferred embodiments. It should be understood that variations andmodifications thereof can be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention.Accordingly, the present invention embraces all such alternatives,modifications and variations that fall within the scope of the appendedclaims.

1. A method of preparing an improved field-effect transistor of the typehaving a source region and a drain region, a channel layer extendingbetween the source region and the drain region, the channel layerincluding a semiconducting organic-inorganic hybrid material, a gateregion disposed in spaced adjacency to the channel layer, anelectrically insulating layer between the gate region and the sourceregion, drain region and channel layer, wherein the improvementcomprises: preparing a channel layer comprising a melt-processedsemiconducting organic-inorganic hybrid material by a process comprisingthe steps of: maintaining a solid organic-inorganic hybrid material at atemperature above the melting point but below the decompositiontemperature of said organic-inorganic hybrid material for a period oftime sufficient to form a uniform melt; and cooling said uniform melt toan ambient temperature under conditions sufficient to produce saidmelt-processed organic-inorganic hybrid material.
 2. The method of claim1, wherein said source region, channel layer and drain region aredisposed upon a surface of a substrate, said electrically insulatinglayer is disposed over said channel layer and extending from said sourceregion to said drain region, and said gate region is disposed over saidelectrically insulating layer.
 3. The method of claim 1, wherein saidgate region is disposed as a gate layer upon a surface of a substrate,said electrically insulating layer is disposed upon said gate layer, andsaid source region, channel layer, and drain region are disposed uponsaid electrically insulating layer.
 4. The method of claim 1, whereinsaid melt-processed organic-inorganic hybrid material is in the form ofa film.
 5. The method of claim 4, wherein said melt-processedorganic-inorganic hybrid material film comprises a single crystal ofsaid organic-inorganic hybrid material.
 6. The process of claim 4,wherein said said melt-processed organic-inorganic hybrid material is apolycrystalline material having a grain size equal to or greater thanthe dimensions between contacts in a semiconductor device.
 7. The methodof claim 1, wherein said organic-inorganic hybrid material has a meltingpoint below its decomposition temperature.
 8. The method of claim 1,wherein said organic-inorganic hybrid material comprises: an inorganicanion layer having a metal-ligand framework; and an organic cation layerhaving an organic cation capable of templating said metal-ligandinorganic anion layers within the organic-inorganic hybrid materialstructure.
 9. The method of claim 8, wherein said metal-ligand frameworkcomprises a metal ligand pair selected from the group consisting of:corner-sharing metal ligand octahedra, corner-sharing metal ligandtetrahedra, corner-sharing metal ligand trigonal bipyramids,face-sharing metal ligand octahedra, face-sharing metal ligandtetrahedra, face-sharing metal ligand trigonal bipyramids, edge-sharingmetal ligand octahedra, edge-sharing metal ligand tetrahedra andedge-sharing metal ligand trigonal bipyramids.
 10. The method of claim9, wherein said metal ligand pair is selected from the group consistingof: metal halide, metal oxide and metal sulfide.
 11. The method of claim8, wherein said organic-inorganic hybrid material is anorganic-inorganic perovskite, comprising alternating layers of: aninorganic anion layer having a metal halide framework of corner-sharingmetal halide octahedra, wherein said metal has a valence n in the rangeof from 2 to 6, said metal halide layer being represented by theformula:(M^(n+))_(2/n)V_((n−2)/n)X₄ ²⁻ wherein M is a metal; V is a vacancy; Xis a halide; and n is an integer in the range of from 2 to 6; and anorganic cation layer having a plurality of organic cations capable oftemplating said metal halide inorganic anion layers within theperovskite structure.
 12. The method of claim 11, wherein said metal isselected from the group consisting of Sn²⁺, Pb²⁺, Ge²⁺, Cu²⁺, Ni²⁺,Co²⁺, Fe²⁺, Mn²⁺, Cr²⁺, V²⁺, Pd²⁺, Cd²⁺, Pt²⁺, Rh²⁺, Eu²⁺, Yb²⁺, Sm²⁺,Bi³⁺, Sb³⁺, In³⁺, Sn⁴⁺, Te⁴⁺, Hf⁴⁺, Nb⁵⁺, Ta⁵⁺, Mo⁵⁺ and a combinationthereof.
 13. The method of claim 12, wherein said metal is selected fromthe group consisting of Sn²⁺, Pb²⁺, Bi³⁺, Sb³⁺, Te⁴⁺ and a combinationthereof.
 14. The method of claim 11 wherein said halide is iodide. 15.The method of claim 11, wherein said organic cation is selected from thegroup consisting of: an organic mono-ammonium cation, an organicdiammonium cation and a combination thereof.
 16. The method of claim 15,wherein said organic mono-ammonium cation is selected from the groupconsisting of: phenethylammonium, 2-fluorophenethylammonium,2-clorophenethylammonium, 2-bromophenethylammonium,3-fluorophenethylammonium, 3-clorophenethylammonium,3-bromophenethylammonium, 4-fluorophenethylammonium,4-clorophenethylammonium, 4-bromophenethylammonium,2,3,4,5,6-pentafluorophenethylammonium and a combination thereof. 17.The method of claim 15, wherein said organic di-ammonium cation isderived from a diamine selected from the group consisting of:1,2-ethylene diamine, 1,3-propylene diamine, 1,4-butylene diamine,bis-(aminoalkyl)-substituted arylene, bis-(aminoalkyl)-substitutedheteroarylene and a combination thereof.
 18. The method of claim 17,wherein said diamine has a string of 2-6 aromatic moieties eachindependently selected from the group consisting of: phenelene,naphthylene, anthracene, phenanthrene, furan and thiophene.
 19. Themethod of claim 15, wherein said organic diammonium cation is obtainedby protonation of5,5′″-bis(aminoethyl)-2,2′:5′,2″:5″,2′″-quaterthiophene.
 20. The methodof claim 1, wherein said cooling to an ambient temperature is carriedout at a rate from about 0.001° C./sec to about 1000° C./sec.
 21. Themethod of claim 20, wherein said cooling to an ambient temperature iscarried out by exposing said uniform melt to a temperature gradient forcontrolling the grain size of said laminated melt-processedorganic-inorganic hybrid material.
 22. An improved field-effecttransistor prepared by the method of claim 1.